This invention relates to an improvement in off-road vehicle transmission systems of the type wherein gearshift levers are mechanically linked to couplers to select ranges of gears, and electro-hydraulic powershift clutches are provided to select one gear within a selected range. More specifically, the present invention provides an improvement in such transmissions to obtain a more uniform automatic selection of the effective gear at the time of start-up.
In the transmission system described in the above-referenced applications, three operator controls are provided for gear selection. A High/Low range shift lever is mechanically linked to a first coupler and selects a first or a second range of gear speeds, each range including 8 gear speeds. A 4/5 range shift lever selects one of two sub-ranges within the range selected by the High/Low shift lever, each sub-range including 4 gear speeds. Finally, two powershift push-buttons are provided for controlling electro-hydraulic clutches to select one of four gear speeds within the range defined by the High/Low and 4/5 range select levers. A microprocessor senses the various operator controls and selects a specific powershift gear when the 4/5 shift lever is shifted. That is, powershift gear 4 is selected when the 4/5 shift lever is shifted from its high range position (5) to its low range position (4) and powershift gear 1 is selected when the shift lever is shifted from its low range position to its high range position.
It will be appreciated that in the described system the gear selected at start-up may vary widely depending on the positions of the range shift levers and the selected powershift gear. Even if the powershift gear selection is limited to the lowest powershift gear, the transmission at start-up could be in gear 1, 5, 9 or 13 depending on the positions of the range shift levers. However, it is desirable that the initial gear selection be as nearly constant as possible within the limits imposed by the positions of the shift levers. Furthermore, it is desirable that the transmission not be engaged until the operator has completed a sequence of actions indicating that he is anticipating engagement of the transmission.